Domain Name System Blocklists (DNSBLs) are spam-blocking lists that allow an email administrator to block messages from specific systems that have a history of sending spam. DNSBLs are based on the Domain Name System (DNS), which makes the lists easier to read, use, and search.
If a DNSBL owner receives spam from a specific IP address, that IP address is blocklisted. Any company that uses the blocklist for spam filtering may block future messages from that IP address or place them into the spam folder.
